U.S. patent number 3,780,724 [Application Number 05/173,604] was granted by the patent office on 1973-12-25 for sensation-cognition computer employing "t" test calculations.
This patent grant is currently assigned to Neuro-Data, Inc.. Invention is credited to Erwin Roy John.
United States Patent |
3,780,724 |
John |
December 25, 1973 |
SENSATION-COGNITION COMPUTER EMPLOYING "t" TEST CALCULATIONS
Abstract
A patient who may be unable to cooperate is tested for auditory,
visual and somatosensory perception. The apparatus includes an
electroencephalograph, programmed stimulators, a t test computer
including an average response computer and a recorder. Evoked
responses of the patient are elicited and the patient's short-term
memory is tested.
Inventors: |
John; Erwin Roy (Riverdale,
NY) |
Assignee: |
Neuro-Data, Inc. (Cliffside
Park, NJ)
|
Family
ID: |
22632779 |
Appl.
No.: |
05/173,604 |
Filed: |
August 20, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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877948 |
Nov 19, 1969 |
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Current U.S.
Class: |
600/544 |
Current CPC
Class: |
A61B
5/316 (20210101); A61B 5/377 (20210101) |
Current International
Class: |
A61B
5/04 (20060101); A61B 5/0476 (20060101); A61B
5/0484 (20060101); A61N 1/36 (20060101);
A61b () |
Field of
Search: |
;128/2.1B,2.1R
;235/150.53,151.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Parent Case Text
This is a continuation-in-part of Application Ser. No. 877,948,
filed Nov. 19, 1969 and now abandoned, and entitled
"Sensation-Cognition Computer."
Claims
I claim:
1. Apparatus for the testing of a subject which includes a
plurality of electrodes adapted to be connected to the head of the
subject to monitor his brainwaves, an amplifier connected to said
electrodes to amplify said brainwaves, an electroencephalograph
connected to said amplifier, switching means connected to said
electroencephalograph, a t test computer whose input is connected
to the output of said electroencephalograph, said computer having a
first squaring circuit, an average response computer having a
plurality of channels and being connected to said first squaring
circuit, a second squaring circuit connected to said average
response computer, a first differential circuit connected to said
average response computer and said second squaring circuit, a first
divider circuit connected to said first differential circuit and to
said average response computer, a summing circuit connected to said
first dividing circuit, a square root circuit connected to said
summing circuit, a second divider circuit connected to said square
root circuit, a second differential circuit connected to said
second divider circuit and to said average response computer, and
an absolute value circuit connected to said second divider circuit,
a recorder connected to said "t" test computer to record the
averaged brainwaves, a programmed timer connected to and
controlling said switching means, and stimulus means connected to
said programmed timer and controlled by it.
2. The apparatus for the testing of a subject as in claim 1 wherein
the programmed timer has stored therein a plurality of alternative
programs and the apparatus includes a program switching mechanism
whereby one of the alternative programs may be selected.
3. The apparatus of claim 1 and including means to set within the t
test computer the number of sample sweeps N and the level of
significance P to provide a "go - no go" signal to said
recorder.
4. The apparatus of claim 1 and also including variable setting
means to set within the t test computer the t test standard value
and the maximum number of sample sweeps N, upon attainment of which
standard t value a control signal is provided by said t test
computer to said programmed timer.
5. An apparatus as in claim 1 wherein within the said t test
computer said first squaring circuit includes two squaring means
and wherein two sampling lines are connected to the output of said
electroencephalograph, the said averaging circuit of said t test
computer is a four-channel average response computer whose inputs
are the said two sampling lines and the said two squaring means,
and the inputs of which said two squaring means are connected to
said sampling lines.
Description
DESCRIPTION
The present invention relates to patient testing and more
particularly to the testing of neural responses to auditory, visual
or sensory stimuli, and to the perception of orderly relationships
between stimuli.
Generally, the testing of auditory, visual or somatosensory systems
requires the voluntary response of the patient. For example, eyes
are examined by showing a chart having characters or pictures. The
person being tested tells what he sees. Similarly, hearing is
tested by presenting varying intensities and frequencies of sound.
The person being tested tells when he can, and cannot, hear the
sounds.
But, if the person being tested cannot or will not cooperate, the
testing becomes difficult. For example, the person being tested may
be an infant or a person unable to speak due to injury or other
causes. Some subjects cannot, or will not, say if they can hear a
noise, see a chart or light, or feel a sensory stimulation.
The present invention provides a method for testing whether
hearing, vision or tactile sensation is impaired, and to determine
the likelihood of mental retardation. The prior art points out the
existence of a widespread interest in the testing of children, more
specifically the testing of infants. In a study by Beasley
(Beasley, W.C. 1933, "Child Development," 4, 106-120, 55-56) an
infant's ability to fix his gaze on a light (stimulus), and to
follow it with his eyes as it moved, was investigated. Beasley
found that infants varied considerably in their ability or
willingness to fix their gaze on an object and further, after
birth, some infants display uncoordinated eye movement.
Another study in this area is that of Marquis (Marquis D.P. 1931,
"Can Conditioned Responses Be Established in the New Born Infant?"
-- Journ. of Genetic Psychology, 39, 479-492, 74-75). Marquis was
concerned with the subject of learning in early infancy, in
particular with the question of whether during the first days of
life an infant could acquire a conditioned response. Infants were
bottle-fed from birth. At each feeding a buzzer was sounded.
Marquis found that at 3 to 6 days the infant test subjects
exhibited many responses related to feeding in response to the
buzzer alone. It should be noted, however, that, since an infant's
response to a stimulus may be generalized, some of the observed
effects might have occurred even if feeding had not been used as
the conditioning stimulus.
In a later study, Marquis (1941-Journ. of Experimental Psychology,
29, 263-282, 68, 75-78) directed his attention to the question of
whether infants learn a feeding schedule within the first 10 days
of life. The body activity of the infant subject was measured with
the aid of a device supporting his bassinet. The results of the
study show that infants on three-hour feeding schedules learned to
expect food at the end of three hours.
Another interesting study in this area is that of Kantrow (Kantrow,
R.W. 1937 -- Studies in Child Welfare, 13, No. 3, Univ. of Iowa
Press 74-75). Kantrow, working with infants ranging in age from
approximately 11/2 to 4 months, found that they learned to respond
to buzzing as a signal for food and, further, that they also
learned to discard false signals, that is, buzzing that no longer
meant food.
The method employed by Kantrow suffers, however, from the
disadvantages common to all of the methods employed in the
aforementioned prior art studies. The immature infant subject can
do little, or nothing, to cooperate with the tester. The tester is
therefore forced to cooperate with his subject. Further, the tester
is forced to gauge the infant subject's response overtly, by what
the infant does when exposed to the stimulus. Reliance upon the
tester's observation of the infant's overt acts introduces the
possibility of human error.
The instant invention attempts to resolve the above-mentioned
disadvantages inherent in the prior art testing methods. In the
method of the invention herein disclosed, the tester does not have
to rely on the test subject's overt responses to a stimulus. Thus,
the element of human error inherent in the prior art methods is
substantially reduced, if not totally eliminated.
The method of the invention contemplates presenting the test
subject with a series of stimuli controlled by a programmed timer.
The electrical responses of the brain to these stimuli are detected
by electrodes attached to the appropriate regions of the head and
amplified by an electro-encephalograph (EEG). The evoked responses
to these stimuli are then extracted from the ongoing EEG activity
by an average response computer (ARC). The significance of the
extracted signal is automatically tested, on a statistical basis,
by a t test computer. The signal, if deemed significant by that
test, is then recorded.
The functional assessment of a particular sensory system is
accomplished by presenting a series of stimuli in that sensory
modality, computing the average evoked response, and determining
its statistical significance. The presence, or absence, of the
evoked response provides an indication of whether the sensory
stimulus caused neural impulses from the peripheral sensory
receptor (eye, ear, skin, etc.) to propagate through the central
nervous system to the cortex. In addition, the detailed waveshape
of the evoked and averaged response may be presented to permit
evaluation of whether the response process includes all of the
electrophysiological features usually considered "normal." For
example, a group of waveshapes may indicate sensory
malfunction.
The instrument provides a functional assessment of the ability of
an individual to perceive orderly relationships between stimulus
patterns, which may be a way to evaluate fundamental cognitive
processes and short-term memory. Five specific methods for
cognitive assessment are presented. The stimulus, to carry out each
method, is presented in a predetermined timed sequence, with the
sequences being programs stored in the programmed timer and
controlling the other circuits of the instrument.
The advantages of the method of the invention described herein are
readily apparent. The early diagnosis of defective vision,
defective hearing, or mental damage affords one the opportunity for
instituting early corrective measures, training or special
care.
Other objectives of the present invention will be apparent from the
following detailed description, describing the inventor's best mode
of practicing the invention, taken in conjunction with the
accompanying drawings. In the drawings;
FIGS. 1, 6 and 8 are block schematic diagrams of two embodiments of
the testing instrument utilized in the methods of the present
invention;
FIGS. 2, 3 3A-3C, 4 and 5 are graphs illustrating a normal brain
wave response to a predicted stimulus and illustrating a normal
brain wave response to an unpredicted stimulus;
FIg. 7 is a chart showing a type of visual stimulus;
FIG. 9 is a block circuit diagram of the t test computer; and
FIGS. 10A, 10B, 11A, 11B, 12 13 and 14 are circuit diagrams of
specific circuits used in the t test computer of FIG. 9.
THE TESTING SYSTEMS
As shown in FIG. 1, the devices used are an electroencephalograph
and programmed stimulators, switches, and an average response
computer. Two contacts 1 and 2 are adapted for connection to the
scalp of the person being tested. The leads 3 and 4 to the
respective contacts 1 and 2 are connected to amplifiers 5 and 6,
respectively. The amplifiers may be preamplifiers to the
electroencephalograph 7. The electroencephalograph 7 is connected
to a switch 14C which is connected to an average response computer
10 which, in turn, is connected to a pen recorder 11 or other
indicating means. A suitable average response computer is described
in Clynes U.S. Pat. No. 3,087,487. A simple stimulus is presented
by the flashing light 13 or the click sounding device 14. Other
stimulating devices are other sound producing devices and a device
which produces a small shock or tap on the skin. The stimulating
devices are controlled as to their sequence and timing by a program
timer 12. Inputs to computer are switched at the proper time by
switch 14 operated by timer 12. The timer 12 is controlled by a
program. Preferably there are a plurality of alternative programs
(five of which are described below) one of which is selected at a
time by the program selector switch 15.
In the embodiment of FIG. 8 the devices used are an
electroencephalograph, programmed stimulators, switches, a recorder
and a t test computer, part of which is an average response
computer. Two contacts 1a and 2a, adapted for connection to the
scalp of the person being tested, have leads 3a and 4a connected to
preamplifiers 5a and 6a respectively. The preamplifiers 5a and 6a
are connected to the electroencephalograph 7a which is connected to
a switch 14b which in turn is connected to a t test computer. The t
test computer 16a is connected to a pen recorder 11a or other
indicating means. The stimulators 13a and 14a are controlled as to
their sequence and timing by program timer 12a and the inputs to
computer 16a are switched at the proper time by switch 14b operated
by timer 12a. As in the other embodiments, the timer 12a is
controlled by a program. Preferably there are available in the
timer 12a a plurality of alternative programs (five of which are
described below) one of which is selected at a time by the program
selector switch 15a. For example, the program may be in the form of
punched holes on a paper or plastic tape, or may be electronic. The
program performs the following functions: (1) it controls each of
the stimulators 13a and 14a so that they operate in the selected
sequence and time, (2) it controls the average response computer so
that it records on the selected channel at the selected time
period.
THE T TEST COMPUTER
The "T" test is a statistical test for a measure of the
significance of the difference between two sample populations. For
example, for a sample size of N = 10, corresponding to 10 sweeps
(ten repetitions of each stimulation), to obtain a level of
significance P of 0.001 (the result occurring by random chance 1 in
1000) the t result must be 4.587. With 25 sweeps and P = 0.001 the
t result is 3.725.
Preferably both the number of sweeps N and the level of
significance may be varied by dials on the t test computer 16a to
set a predetermined t test standard. For example, the tester may
set the maximum number of sweeps N at 25 and the level of
significance P at 0.001. For each stimulus group either the t test
of the evoked response (X values) compared to brain wave ongoing
activity background (Y values), will exceed 3.725 (the
predetermined t standard) or be less than 3.725. If the t test
evoked response result is larger than the standard, then there is
only 1 in 1000 chance that the result was by accident and
consequently the test shows that the subject very likely responded
to the stimulus. Upon such t test result, the recorder 11a will
record the presence of a response.
Preferably the t test computer will send out its result to recorder
11a as soon as the predetermined t test standard is reached, even
though the standard is reached before the maximum set number of
sweeps. For example, if N is set at 25 and the P set at 3.725 and
the P value is exceeded on the 11th sweep, a control signal on line
15' will be sent and the remaining 14 sweeps omitted, since a
satisfactory set of evoked responses has been obtained.
Alternatively, at less cost, the t test computer 16a may be set at
the factory to perform a fixed number of sweeps P to obtain a fixed
value of t, thereby setting the level of significance. In this
alternative, at each stimulation a "go-no go" signal would be
shown, for example, by the pen recorder or by a light.
The preferred embodiment of the t test computer is shown in FIG. 9.
As shown, the computer has two inputs -- an X input on line 100 and
a Y input on line 101. The inputs 100 and 101 are to a two-channel
sample and hold circuit 102. The purpose of the sample and hold
circuit 102 is to sample the two signals X and Y and to hold them
so that they become in phase. A suitable sample and hold circuit is
shown in FIG. 10A. The output lines 103 and 104 of the sample and
hold circuit 102 are each directly connected to one channel of a
four-channel average response computer 105. In addition, the
outputs 103 and 104 are connected to respective squaring circuits
106 and 107, the details of the squaring circuit being given in
connection with FIG. 12. The average response computer 105 gives a
value of samples taken periodically in time divided by the number
of samples, thereby providing a running average, that is, an
average which changes with the additional samples. A suitable
average response computer is described in Clynes U.S. Pat. No.
3,087,487. The number of samples N is determined by the sampling
rate which is set by the clock pulses produced by an internal
clock, such as a crystal controlled oscillator whose output is
divided, within the average response computer 105. The output of
the first channel 108 is the average of the sum of the values of X,
i.e., the sum of the voltages of each of the samples divided by the
number of the samples N, which is the mean and may be expressed by
the formula: (.SIGMA.X/N.sub.x)=M.sub.1 The output of the channel
109 of the average response computer 105 is the sum of the X values
squared over the number of samples and may be expressed by the
formula: (.SIGMA.X.sup.2 /N.sub.x) The output of channel 110 is the
sum of the Y values over the number of samples and may be expressed
by the formula: (.SIGMA.Y/N.sub.y)=M.sub.2 and the output of
channel 110' the sum of the Y values squared over the number of
samples and may be expressed by the formula: (.SIGMA.Y.sup.2
/N.sub.y).
Each of the channels is connected to a four-channel sample and hold
circuit 111. The only purpose of the sample and hold circuit 111 is
to permit the use of a single digitizer with the average response
computer 105 and to sample the results. An alternative is to have a
digitizer for each of the channels, in which case the sample and
hold circuit 111 would not be necessary. The circuits of each of
the four channels of the sample and hold circuit 111 are the same
as the sample and hold circuit shown in FIG. 10A.
The output of channel 108, which is the mean, is then squared in a
squaring circuit 112 and similarly the output of channel 110 is
squared in a squaring circuit 113. Each of the squaring circuits is
the same as shown in FIG. 10B. The output of the squaring circuit
and the output of channel 109 are then combined in a differential
amplifier 114. Similarly the outputs of the squaring circuit 113
and channel 110' are combined in differential amplifier 115. The
detailed circuit of a suitable differential amplifier is shown in
FIG. 11A. The formula for the computation which occurs in the
differential amplifier 114 is: (.SIGMA.X.sup.2 /N.sub.x
-(.SIGMA.X/N.sub.x).sup.2 = 6.sub.x.sup.2 and the formula for the
mathematical computation which occurs in the differential amplifier
115 is (.SIGMA.Y.sup.2 /N.sub.y)-(.SIGMA.Y/N.sub.y).sup.2
=6.sub.y.sup.2
The outputs of the differential amplifiers are connected to the
respective divide circuits 116 and 117, the details of which are
shown in FIG.12. The divide circuit 116 divides the deviation
6.sub.x.sup.2 by the number of samples. The output of the divide
circuits 116 and 117 are connected to summing amplifier (adder) 118
which performs the following mathematical computation:
(6.sub.x.sup.2 /N.sub.x) + (6.sub.y.sup.2 /N.sub.y), a suitable
circuit being shown in FIG. 11B. The output of the summing
amplifier 118 is to a square root circuit 119, the details of which
are given in FIG.12 The output of the square root circuit is to the
divide circuit 12 a suitable divide circuit being shown in FIG.12.
The second input to the divide circuit is from a differential
amplifier 121 which may be of the type shown in FIG.11A. The
differential amplifier 121 provides the difference between the two
means, that is, it accomplishes the mathematical computation as
follows: (.SIGMA.X/Nx) - (.SIGMA.y/Ny) The output of the divide
circuit 120 is to the absolute value circuit 121, shown in FIG. 13
which provides the final result of the t test.
All of the computations necessary for the t test have been provided
by the circuit of FIG. 9 and the t test result is taken at the
output 123. The t test computation performed by the circuit of
FIG.9 is as follows: ##SPC1##
A suitable squaring circuit, as shown in FIG. 10B, uses three
integrated circuits. The integrated circuits 150 and 151 are
operational amplifiers and may be of the type Motorola No. MC
1556-G. That integrated circuit is a compensated and monolithic
operational amplifier. The integrated circuit 152 is a multiplier
which, suitably, may be Motorola Type 1594-L. The multiplier, as
its two inputs 153 and 154 derived from a common line 155 which is
the output of the operational amplifier 150, and acts to square the
input from line 155; that is, its inputs are tied together. A
suitable integrated circuit is a monolithic four-quadrant
multiplier where the output voltages are a linear product of two
input voltages. The Motorola 1594-L is a variable transconductance
multiplier with internal level shift circuitry and voltage
regulation. The scale factor is adjustable and preferably is set to
be one-tenth of input. An operational amplifier 151 is used to
complete the multiplier connections from the integrated circuit
152. Its output 156 provides a square of the input at 157. This
type of multiplier connection is described in further detail in the
specification sheet dated Oct. 1970 DS-9163 from Motorola of
Phoenix, Arizona, of their 1594-L integrated circuit.
A suitable sample and hold circuit is shown in FIG. 10A. It uses an
operational amplifier 140. Preferably operational amplifier 140 is
an integrated circuit, for example, of the type Motorola No. 1456G,
described above.
A suitable differential amplifier circuit is shown in FIG. 11A. It
uses an operational amplifier 160 having two inputs 161 and 162.
Preferably the operational amplifier 160 is an integrated circuit.
A suitable integrated circuit is Motorola No. MC 1456G described in
the specification sheet DS9147R1 dated Apr. 1970 as being epitaxial
passivated and monolithic. It has a power supply voltage of +18V dc
and -18V dc, a power bandwidth of 40K Hz and power consumption of
45m W max.
The summing amplifier of FIG.11B also uses an operational amplifier
165. The two inputs to be added are connected to one input of the
amplifier 165. A suitable operational amplifier is the integrated
circuit Motorola No. 1456G described above.
A suitable divider circuit is shown in FIG. 12. It uses a linear
multiplier 170 and an operational amplifier 171. Preferably the
multiplier 170 and the amplifier 171 are integrated circuits. A
suitable integrated circuit for the multiplier 170 is Motorola No.
1594, described above, and for the amplifier Motorola No. 1456G,
also described above. The inputs are 172 and 173 and the output at
174.
A suitable square root circuit is shown in FIG. 14. The square root
circuit is a special case of a divider in which the two inputs to
the multiplier are connected together. Consequently the input line
173 and the input line 172 are connected together to form a common
input line 175.
A suitable absolute value circuit is shown in FIG. 13. It uses two
operational amplifiers 176 and 177. Preferably they are integrated
circuits and may be of the type Motorola No. 1456G described above.
The input 178 is to the minus input of amplifier 176 and the output
179 is from amplifier 177. The purpose of the circuit of FIG. 13 is
to provide a quantity regardless if the X or the Y terms are
larger, the absolute value being the value regardless of the plus
or minus sign of the quantity.
THE PROGRAMMED TESTING METHODS
In the firet method, an alternating series of flashes (F) and
clicks (C) are presented as follows: F, C, F, C, F, C, F, C, F, C,
F, C, etc., until some 200 presentations of each stimulus have
occurred. As the programmed stimulator presents this alternating
sequence, the evoked responses are alternately directed to two
different channels of the average response computer (ARC), one
computing the visual evoked response (VER), the other computing the
auditory evoked response (AER). The regular alternation of visual
and auditory stimuli constitutes a completely predictable sensory
pattern. The VER and AER resulting from such predictable
stimulation are recorded in any acceptable fashion: photograph, ink
record, electronic memory device. Now a second sequence of 200
flashes and clicks is presented, but the different sensory stimuli
are in random sequence, as for example:
F, c, f, f, c, f, c, c, c, f, c, f, cc, f, f, f, etc.
As the programmed stimulator presents this random sequence, the
evoked responses are appropriately switched to two different
channels of the ARC, and the VER and AER are again computed. This
random) sequence constitutes a completely unpredictable sensory
pattern.
Visual evoked responses (VER's) and auditory evoked responses
(AER's) from predictable and unpredictable stimulus sequences are
then compared. The finding of marked differences between the
responses elicited by predictable and unpredictable stimuli would
strongly suggest that the subject perceived the alternating pattern
as an orderly series of events. That perception is a cognitive
process, involving short-term memory. Differences in evoked
responses to predictable and unpredictable events would be expected
to appear especially in the period from 100 to 300 milliseconds
after the stimulus and are illustrated in FIG. 2. Study of the
details of differences might provide information about the cause of
the cognitive deficit.
The second method for assessing cognitive process is to establish a
predictable pattern of stimulation and abruptly alter it. For
example, F--F, F--F, F--F, F--F, F--. . . . Computation of the VER
at the time of the omitted flash would reveal a potential evoked by
the absent but predicted event.
In the charts of FIG. 3, waveforms of different test patients are
shown, the time is in milliseconds and the output in microvolts.
These charts are an illustration of the second method. In the
waveform A, a flash and its evoked response occurs at points 21,
22, 23, 24, 25 and 26. This shows the normal response to the flash.
Waveform B shows a flash and its evoked response at 31, 32, 33, 34
and 35. At 36 there is no flash, but the subject's short-term
memory has the expectation of a flash and shows the same waveform
as if the flash occurred. This is the normal response In waveform C
the flash and its evoked response are at points 41, 42, 43, 44 and
45. At point 46 no flash occurs and there is no response and no
short-term memory. This is an abnormal response and indicates the
absence of short-term memory. Such an absence may, for example, be
associated with brain damage.
As another example of a suitable pattern using the second method, a
flash and a "click" sound may constitute a pair of stimuli. The
pattern, with 5 seconds of rest between eahc pair, would be as
follows: click-flash-(5seconds rest); click-flash-(5 seconds rest);
click-flash-(5 seconds rest); click-flash-(5 seconds rest); click.
The brain wave would then be examined for the presence or absence
of the expectancy of the omitted "flash" from the last pair of
stimuli.
A third method consists of presenting the same stimulus in repeated
blocks of 100 trials. For example, a 2 per second flickering light
is presented for 50 seconds and the average response is computed in
one channel of the ARC. After a 10-second pause, the 2 per second
flicker is again presented for 50 seconds and an average response
computed in the second channel of the ARC. After 10 seconds,
another 100 flashes at 2 per second are averaged in the third
channel. After 10 seconds, a buzzer sounds and a 5 per second
flicker is presented for 20 seconds and the response averaged in
the fourth channel.
The normal subject will show a progressive diminution to the
repeated presentation of the same stimulus, due to habituation to a
meaningless event. Thus the third average response will be smaller
than the second, which will be smaller than the first. Presentation
of the buzzer will cause dishabituation, and this will be further
increased by the change in stimulus frequency, causing a marked
increase in the size of the fourth average. In abnormal subjects,
habituation will be slower or absent and dishabituation will not
occur, as seen in FIG. 4.
A fourth method consists of sensory-sensory conditioning. The
response from the occipital area of the head, over the visual
cortex, is utilized. A click control average response is obtained
in one channel of the ARC, while 50 clicks are presented at the
rate of 1 per second. A click plush flash control average response
is then obtained in a second channel of the ARC, while 50
simultaneous click-flash paired stimuli are presented. A
conditioning period then intervenes,during which 300 events occur.
Each event consists of click alone, followed 250 milliseconds later
by click plus flash. The interval between the click plus flash of
each event and the click of the following event is one second.
After the completion of the conditioning period, a test period
occurs. The test period consists of 50 events each composed of
click alone, followed 250 milliseconds later by click plus flash.
By electronic switching, the response to click alone is averaged in
a third channel of the ARC, while the response to click plus flash
is averaged in the fourth channel. Comparison of channel one with
channel 3 and of channel 2 with channel 4 reveals whether the
conditioning procedure has altered the response of the visual
cortex to the click. Changes will be observed in normal but not in
abnormal subjects. The failure of abnormal subjects to show change
may be due to a diffuse deficit in cognitive processes such as
might occur in a mentally retarded child, or may be due to a
specific deficit in associational mechanisms such as might occur in
a child with an epileptic focus in the auditory cortex. By
appropriate variation of the sensory modality of the first and
second stimuli comprising the conditioned stimulus (FIRST) and
unconditioned stimulus (SECOND) of a stimulus pair, it would be
possible to discriminate between diffuse and specific deficits,
accomplishing differential diagnosis. This method is illustrated in
FIG. 5.
The fifth method involves the presentation of stimulus sequences
which share a common pattern although varying in their specific
stimulus composition, and searching for invariant features in the
evoked response. For example, a large square figure is briefly
shown on a screen to the subject, followed by a small square
figure. The stimulator consists of a slide projector 50 which
rapidly changes the slides being projected on screen 51, as shown
in FIG. 6. That sequence of large square followed by small square
is repeated, for example, for 30-100 times. The subject's brain
wave response to these two stimuli is averaged in channels 1
(large) and 2 (small) in the average response computer 10 which
reduces the adverse effects of noise. The results are recorded on
recorder 11. Subsequently a large round figure is shown, followed
by a small round figure. That pattern is rapidly repeated and the
brainwaves averaged and recorded as before, with large circles in
channel 3 and small circles in channel 4.
The recorded brainwaves from the two patterns are then compared. If
the subject perceives squares and circles as different, two
different waveshapes, corresponding to the two stimuli, will be
recorded. That itself is a test of visual cognition. If the subject
is of normal intelligence, for example, a young non-reading child
of normal intelligence, then the recorded brainwave pattern for the
first set (large and small square shapes) will differ from the
recorded brainwave pattern for the second set (large and small
round shape). Further, the normal person recognizes the similarity
of shape (squareness vs. roundness) and tends to disregard the
dissimilarity of size. His brain waves correspond with that
recognition. Therefore, channel 1 will resemble channel 2 and
channel 3 will resemble channel 4. In contrast, a non-normal
subject may perceive squares and circles as the same, or may fail
to perceive large and small figures as similar, although their
shape is the same (FIG. 7). The presentation of figures and the
recording of the resulting brain wave is therefore a test of normal
pattern perception. Such normal pattern response may be a
prerequisite for reading or normal development. Its lack denotes
that the subject may require special forms of training and
care.
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